Field of the Invention
The present invention relates to an image processing apparatus and an image processing method.
Description of the Related Art
In recent years, for image capturing apparatuses such as those for digital video or the like, the image data amount handled in a system has increased significantly in accompaniment of an increase in resolution and an increase in frame rates, and there is demand for acceleration of image memory and bus interface circuits. With respect to this, it is possible to handle demand for circuit acceleration by reducing the image data amount by performing compression encoding of image data for image memory and for a bus interface.
In such a case, it is desired that the encoding scheme for image compression have a small circuit scale, and a short encoding delay. Therefore, it is unsuitable in conventional DCT-based encoding schemes as typified by the JPEG and MPEG2. Accordingly, a proposal has been made for a DPCM (Differential Pulse Code Modulation) based predictive encoding scheme (refer to Japanese Patent Laid-Open No. 2010-004514).
In a DPCM-based predictive encoding scheme, a degradation of image quality tends to occur at an edge portion where a change in pixel levels is large. In the proposed scheme of Japanese Patent Laid-Open No. 2010-004514, encoding with low image quality degradation is possible if a difference in values between adjacent pixel data is less than or equal to a predetermined threshold. However, if the difference in values between adjacent pixel data exceeds a predetermined threshold as with a sharp edge portion, it is necessary to half the original pixel data bits by quantization (for example, to turn 10 bits into 5 bits), and this becomes a major cause of image quality degradation. Similarly, it becomes a major cause of image quality degradation if the difference between a predicted image and an encoding target image is large.